Semiconductor processing and packaging techniques are continually evolving to meet industry demands for improved performance with reduced size and cost. Electronic products require packaged semiconductor assemblies with a high density of devices in a relatively small space. For example, the space available for memory devices, processors, displays and other microfeature devices is continually decreasing in personal electronic devices such as cell phones, laptop computers and many other products. Accordingly, a need exists to decrease the overall size of the microfeature devices while still maintaining or improving performance and reducing cost.
One technique used to improve the performance and reduce the size and cost of these microfeature devices involves wafer level packaging (“WLP”). WLP generally refers to the packaging of microfeature devices at the wafer level, rather than processing and packaging individual devices after dicing them from a wafer. One benefit of WLP is that it creates chip-sized packages having the smallest form factor. WLP achieves these small sizes by limiting components of the package, such as interconnect elements, to be within the footprint or fan-in area of the device. These components are limited within the device footprint because the components are formed at the wafer level before the devices are singulated. WLP also provides the benefit of producing packages having excellent electrical and thermal performance due to the overall reduced size of the package and relatively short length of the interconnects. Additional advantages provided by WLP include the ease of fabrication and reduced assembly cost due to simultaneous or parallel processing and testing at the wafer level. Even though WLP may provide the benefits listed above, it may not be suitable for devices having high pin counts or high input/output requirements. For example, the space limitation of the device footprint restricts the number and pitch of the interconnect elements in the package.
To overcome this problem, the dies can be diced and plated in built-up packages that include interconnects which surround the die and extend through a molded polymer. Although positioning these interconnects outside of the footprint of the die can increase the number and/or pitch of the interconnects, it can significantly increase the cost and complexity of the processing. For example, in certain circumstances the filling process can trap air in the via that can cause the interconnect or package to crack as the fill material and the package harden. Such non-uniformities in the vias provide inconsistent electrical connections and compromise the integrity of the interconnects and performance of the package. Additionally, forming the vias by ablation or drilling processes typically requires forming individual vias in a sequential manner, thus increasing the processing time. Simultaneously forming the vias by an etching process can be much faster, but etching can result in inconsistent via sizes. It can also be difficult to achieve a dense distribution of the vias with an etching process. Moreover, the plating and filling processing steps following the via formation require additional processing time.